1. Field of the Invention
The present invention relates generally to a probe card assembly, and more specifically to achieving a more planar relationship between the contact elements on a probe card assembly and a device under test.
2. Background Information
Individual semiconductor devices (dies) are typically produced by creating several identical devices on a semiconductor wafer, using commonly known techniques such as photolithography and deposition. Generally, these processes are intended to create fully functional integrated circuit devices, prior to separating the individual dies from the semiconductor wafer. However, physical defects in the wafer and defects in the processing of the wafer often lead to the presence of some defective dies on the wafer. It is desirable to be able to identify the defective dies prior to packaging or prior to their separation from the wafer. To perform such identification, wafer testers or probers are used to make pressure connections to connection pads (bond pads) on the dies. The dies can then be tested for defects. A conventional component of a wafer tester is a probe card which has contact elements that effect the pressure connections to the bond pads of the dies.
A probe card can be part of a probe card assembly, such as that which is described in U.S. Pat. No. 5,974,662, titled “Method of Planarizing Tips of Probe Elements of a Probe Card Assembly,” which is incorporated by reference herein. A probe card assembly according to U.S. Pat. No. 5,974,662 typically includes a number of components in addition to the probe card itself, such as an interposer and a space transformer. The interposer is disposed between the probe card and the space transformer and allows the orientation of the space transformer to be adjusted relative to the orientation of the probe card.
The space transformer permits a plurality of contact structures on one side of the space transformer to make contact with the terminals of an electronic component (e.g. bond pads on a semiconductor device) at a relatively fine pitch, while connections to another side of the space transformer are made at a relatively coarser pitch. In a preferred embodiment, the contact structures make contact with an active semiconductor device, such as a wafer. Such connections can be disrupted by slight variations in the planarity of the space transformer. Unfortunately, variations in the planarity of the space transformer can occur, for example, when the space transformer is manufactured. For example, an edge of the space transformer might be bent slightly or the center of the space transformer might be bowed.
FIG. 1 illustrates generally a prior art technique for adjusting the orientation of a space transformer. A space transformer 110 is shown with different sets of adjustment points on the bottom of space transformer 110. In one example, the adjustment points correspond to the locations of ball bearings that can be pressed against a back surface of space transformer 110 to adjust the orientation of space transformer 110. In FIG. 1, three adjustment points 112a-112c are used to adjust the orientation of space transformer 110. Adjustment points 112a-112c are located along the periphery of space transformer 110.
The adjustment points shown in FIG. 1 can be used to deflect peripheral areas of space transformer 110, but they cannot be used to deflect non-peripheral areas, such as the center, of space transformer 110. The three points of adjustment shown in FIG. 1 define a plane which is approximately parallel to the plane of a front surface of space transformer 110. However, because there are only three adjustment points, they can adjust the orientation, but not the shape, of space transformer 110; geometric changes are made on only a low order (1st order polynomial). Furthermore, using ball bearings in conjunction with the adjustment points provides for the application of only a pushing force against space transformer 110, and in some instances, the pushing force is opposed by a spring member on an opposite side of space transformer 110.
In many instances, it is desirable to be able to apply a pulling or pushing force at a multiplicity of locations on a space transformer because the space transformer may require deflection or distortion over its surface to achieve better planarity and correct surface variations.